Custom PSScriptAnalyzer Rules

UnderscoreNotAllowedInFunctionName.psm1

<#
    .SYNOPSIS
    Do not use underscores in command names
    .DESCRIPTION
    You should not use underscores in PowerShell command names
    To fix a violation of this rule, rename your command to remove underscores.
    .EXAMPLE
    Measure-UnderscoreNotAllowedInFunctionName -ScriptBlockAst $ScriptBlockAst
    .INPUTS
    [System.Management.Automation.Language.ScriptBlockAst]
    .OUTPUTS
    [Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.DiagnosticRecord[]]
    .NOTES
    None
#>
function Measure-UnderscoreNotAllowedInFunctionName
{
    [CmdletBinding()]
    [OutputType([Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.DiagnosticRecord[]])]
    Param
    (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [System.Management.Automation.Language.ScriptBlockAst]
        $ScriptBlockAst
    )

    Process
    {
        [Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.DiagnosticRecord[]]$results = @()
        try
        {
            #region Define predicates to find ASTs.
            [ScriptBlock]$functionDefinitionWithUnderScores = {
                param ([System.Management.Automation.Language.Ast]$Ast)
                [bool]$returnValue = $false
                if ($funcAst = $Ast -as [System.Management.Automation.Language.FunctionDefinitionAst])
                {
                    # members are part of a class, this rule only applies to bare functions
                    if ($funcAst.Parent -is [System.Management.Automation.Language.MemberAst])
                    {
                        return $false
                    }
                    if ($funcAst.Name -match "_")
                    {
                        return $true
                    }
                }
            }
            #endregion
            #region Finds ASTs that match the predicates.
            [System.Management.Automation.Language.Ast[]]$functionAst     = $ScriptBlockAst.FindAll($functionDefinitionWithUnderScores, $true)

            if (($functionAst.Count -ne 0))
            {
                foreach($extent in $functionAst.Extent) {
                    $result = [Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.DiagnosticRecord]@{
                        'Message' = "Command name '$($functionAst.Name)' should not contain underscores"
                        'Extent' = $Extent
                        'RuleName' = $PSCmdlet.MyInvocation.InvocationName -replace "Measure-"
                        'Severity' = 'Warning'
                    }
                    $results += $result
                }
            }

            return $results
            #endregion
        }
        catch
        {
            $PSCmdlet.ThrowTerminatingError($_)
        }
    }
}